Multiple transcription factors, including BLIMP-1, Eomes, FOXO1, NFATc1, NF-κB, STAT3, STAT4 and T-Bet have been shown to directly regulate PD-1 expression in T cells at various cellular contexts in virus-infected and tumor-bearing hosts [15,17,27,28,29,30,31,32]. This evidence concerns the gene PDCD1 and neoplasm.